/*	$NetBSD: fts.c,v 1.48 2015/01/29 15:55:21 manu Exp $	*/

/*-
 * Copyright (c) 1990, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#if defined(LIBC_SCCS) && !defined(lint)
#if 0
static char sccsid[] = "@(#)fts.c	8.6 (Berkeley) 8/14/94";
#else
__RCSID("$NetBSD: fts.c,v 1.48 2015/01/29 15:55:21 manu Exp $");
#endif
#endif /* LIBC_SCCS and not lint */

#include "config.h"

#include <sys/param.h>
#include <sys/stat.h>

#include <assert.h>
#define _DIAGASSERT(e)
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include "fts.h"
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <stdio.h>

#if !defined(HAVE_DECL_MAX) || (HAVE_DECL_MAX == 0)
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#endif

#if !defined(UINT_MAX) && (HAVE_DECL_UINTMAX_MAX == 1)
#define UINT_MAX UINTMAX_MAX
#endif

#if !defined(HAVE_DIRFD)
#if defined(HAVE_DIR_DD_FD)
#define dirfd(dirp) ((dirp)->dd_fd)
#endif
#if defined(HAVE_DIR_D_FD)
#define dirfd(dirp) ((dirp)->d_fd)
#endif
#endif

static FTSENT *fts_alloc(FTS *, const char *, size_t);
static FTSENT *fts_build(FTS *, int);
static void fts_free(FTSENT *);
static void fts_lfree(FTSENT *);
static void fts_load(FTS *, FTSENT *);
static size_t fts_maxarglen(char *const *);
static size_t fts_pow2(size_t);
static int fts_palloc(FTS *, size_t);
static void fts_padjust(FTS *, FTSENT *);
static FTSENT *fts_sort(FTS *, FTSENT *, size_t);
static unsigned short fts_stat(FTS *, FTSENT *, int);
static int fts_safe_changedir(const FTS *, const FTSENT *, int, const char *);

#if defined(ALIGNBYTES) && defined(ALIGN)
#define FTS_ALLOC_ALIGNED 1
#else
#undef FTS_ALLOC_ALIGNED
#endif

#ifndef ftsent_namelen_truncate
#define ftsent_namelen_truncate(a) \
  ((a) > UINT_MAX ? UINT_MAX : (unsigned int)(a))
#endif
#ifndef ftsent_pathlen_truncate
#define ftsent_pathlen_truncate(a) \
  ((a) > UINT_MAX ? UINT_MAX : (unsigned int)(a))
#endif
#ifndef fts_pathlen_truncate
#define fts_pathlen_truncate(a) ((a) > UINT_MAX ? UINT_MAX : (unsigned int)(a))
#endif
#ifndef fts_nitems_truncate
#define fts_nitems_truncate(a) ((a) > UINT_MAX ? UINT_MAX : (unsigned int)(a))
#endif

#define ISDOT(a) (a[0] == '.' && (!a[1] || (a[1] == '.' && !a[2])))

#define CLR(opt) (sp->fts_options &= ~(opt))
#define ISSET(opt) (sp->fts_options & (opt))
#define SET(opt) (sp->fts_options |= (opt))

#define CHDIR(sp, path) (!ISSET(FTS_NOCHDIR) && chdir(path))
#define FCHDIR(sp, fd) (!ISSET(FTS_NOCHDIR) && fchdir(fd))

/* fts_build flags */
#define BCHILD 1 /* fts_children */
#define BNAMES 2 /* fts_children, names only */
#define BREAD 3  /* fts_read */

#ifndef DTF_HIDEW
#undef FTS_WHITEOUT
#endif

FTS *fts_open(char *const *argv, int options,
              int (*compar)(const FTSENT **, const FTSENT **)) {
  FTS *sp;
  FTSENT *p, *root;
  size_t nitems;
  FTSENT *parent, *tmp = NULL; /* pacify gcc */
  size_t len;

  _DIAGASSERT(argv != NULL);

  /* Options check. */
  if (options & ~FTS_OPTIONMASK) {
    errno = EINVAL;
    return (NULL);
  }

  /* Allocate/initialize the stream */
  if ((sp = malloc(sizeof(FTS))) == NULL) return (NULL);
  memset(sp, 0, sizeof(FTS));
  sp->fts_compar = compar;
  sp->fts_options = options;

  /* Logical walks turn on NOCHDIR; symbolic links are too hard. */
  if (ISSET(FTS_LOGICAL)) SET(FTS_NOCHDIR);

  /*
   * Start out with 1K of path space, and enough, in any case,
   * to hold the user's paths.
   */
  if (fts_palloc(sp, MAX(fts_maxarglen(argv), MAXPATHLEN))) goto mem1;

  /* Allocate/initialize root's parent. */
  if ((parent = fts_alloc(sp, "", 0)) == NULL) goto mem2;
  parent->fts_level = FTS_ROOTPARENTLEVEL;

  /* Allocate/initialize root(s). */
  for (root = NULL, nitems = 0; *argv; ++argv, ++nitems) {
    /* Don't allow zero-length paths. */
    if ((len = strlen(*argv)) == 0) {
      errno = ENOENT;
      goto mem3;
    }

    if ((p = fts_alloc(sp, *argv, len)) == NULL) goto mem3;
    p->fts_level = FTS_ROOTLEVEL;
    p->fts_parent = parent;
    p->fts_accpath = p->fts_name;
    p->fts_info = fts_stat(sp, p, ISSET(FTS_COMFOLLOW));

    /* Command-line "." and ".." are real directories. */
    if (p->fts_info == FTS_DOT) p->fts_info = FTS_D;

    /*
     * If comparison routine supplied, traverse in sorted
     * order; otherwise traverse in the order specified.
     */
    if (compar) {
      p->fts_link = root;
      root = p;
    } else {
      p->fts_link = NULL;
      if (root == NULL)
        tmp = root = p;
      else {
        tmp->fts_link = p;
        tmp = p;
      }
    }
  }
  if (compar && nitems > 1) root = fts_sort(sp, root, nitems);

  /*
   * Allocate a dummy pointer and make fts_read think that we've just
   * finished the node before the root(s); set p->fts_info to FTS_INIT
   * so that everything about the "current" node is ignored.
   */
  if ((sp->fts_cur = fts_alloc(sp, "", 0)) == NULL) goto mem3;
  sp->fts_cur->fts_link = root;
  sp->fts_cur->fts_info = FTS_INIT;

  /*
   * If using chdir(2), grab a file descriptor pointing to dot to ensure
   * that we can get back here; this could be avoided for some paths,
   * but almost certainly not worth the effort.  Slashes, symbolic links,
   * and ".." are all fairly nasty problems.  Note, if we can't get the
   * descriptor we run anyway, just more slowly.
   */
#ifndef O_CLOEXEC
#define O_CLOEXEC 0
#endif
  if (!ISSET(FTS_NOCHDIR)) {
    if ((sp->fts_rfd = open(".", O_RDONLY | O_CLOEXEC, 0)) == -1)
      SET(FTS_NOCHDIR);
  }

  if (nitems == 0) fts_free(parent);

  return (sp);

mem3:
  fts_lfree(root);
  fts_free(parent);
mem2:
  free(sp->fts_path);
mem1:
  free(sp);
  return (NULL);
}

static void fts_load(FTS *sp, FTSENT *p) {
  size_t len;
  char *cp;

  _DIAGASSERT(sp != NULL);
  _DIAGASSERT(p != NULL);

  /*
   * Load the stream structure for the next traversal.  Since we don't
   * actually enter the directory until after the preorder visit, set
   * the fts_accpath field specially so the chdir gets done to the right
   * place and the user can access the first node.  From fts_open it's
   * known that the path will fit.
   */
  len = p->fts_pathlen = p->fts_namelen;
  memmove(sp->fts_path, p->fts_name, len + 1);
  if ((cp = strrchr(p->fts_name, '/')) && (cp != p->fts_name || cp[1])) {
    len = strlen(++cp);
    memmove(p->fts_name, cp, len + 1);
    p->fts_namelen = ftsent_namelen_truncate(len);
  }
  p->fts_accpath = p->fts_path = sp->fts_path;
  sp->fts_dev = p->fts_dev;
}

int fts_close(FTS *sp) {
  FTSENT *freep, *p;
  int saved_errno = 0;

  _DIAGASSERT(sp != NULL);

  /*
   * This still works if we haven't read anything -- the dummy structure
   * points to the root list, so we step through to the end of the root
   * list which has a valid parent pointer.
   */
  if (sp->fts_cur) {
    if (sp->fts_cur->fts_flags & FTS_SYMFOLLOW)
      (void)close(sp->fts_cur->fts_symfd);
    for (p = sp->fts_cur; p->fts_level >= FTS_ROOTLEVEL;) {
      freep = p;
      p = p->fts_link ? p->fts_link : p->fts_parent;
      fts_free(freep);
    }
    fts_free(p);
  }

  /* Free up child linked list, sort array, path buffer. */
  if (sp->fts_child) fts_lfree(sp->fts_child);
  if (sp->fts_array) free(sp->fts_array);
  free(sp->fts_path);

  /* Return to original directory, save errno if necessary. */
  if (!ISSET(FTS_NOCHDIR)) {
    if (fchdir(sp->fts_rfd) == -1) saved_errno = errno;
    (void)close(sp->fts_rfd);
  }

  /* Free up the stream pointer. */
  free(sp);
  if (saved_errno) {
    errno = saved_errno;
    return -1;
  }

  return 0;
}

#if !defined(__FTS_COMPAT_TAILINGSLASH)

/*
 * Special case of "/" at the end of the path so that slashes aren't
 * appended which would cause paths to be written as "....//foo".
 */
#define NAPPEND(p) \
  (p->fts_path[p->fts_pathlen - 1] == '/' ? p->fts_pathlen - 1 : p->fts_pathlen)

#else /* !defined(__FTS_COMPAT_TAILINGSLASH) */

/*
 * compatibility with the old behaviour.
 *
 * Special case a root of "/" so that slashes aren't appended which would
 * cause paths to be written as "//foo".
 */

#define NAPPEND(p)                                         \
  (p->fts_level == FTS_ROOTLEVEL && p->fts_pathlen == 1 && \
           p->fts_path[0] == '/'                           \
       ? 0                                                 \
       : p->fts_pathlen)

#endif /* !defined(__FTS_COMPAT_TAILINGSLASH) */

FTSENT *fts_read(FTS *sp) {
  FTSENT *p, *tmp;
  int instr;
  char *t;
  int saved_errno;

  _DIAGASSERT(sp != NULL);

  /* If finished or unrecoverable error, return NULL. */
  if (sp->fts_cur == NULL || ISSET(FTS_STOP)) return (NULL);

  /* Set current node pointer. */
  p = sp->fts_cur;

  /* Save and zero out user instructions. */
  instr = p->fts_instr;
  p->fts_instr = FTS_NOINSTR;

  /* Any type of file may be re-visited; re-stat and re-turn. */
  if (instr == FTS_AGAIN) {
    p->fts_info = fts_stat(sp, p, 0);
    return (p);
  }

  /*
   * Following a symlink -- SLNONE test allows application to see
   * SLNONE and recover.  If indirecting through a symlink, have
   * keep a pointer to current location.  If unable to get that
   * pointer, follow fails.
   */
  if (instr == FTS_FOLLOW &&
      (p->fts_info == FTS_SL || p->fts_info == FTS_SLNONE)) {
    p->fts_info = fts_stat(sp, p, 1);
    if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
      if ((p->fts_symfd = open(".", O_RDONLY | O_CLOEXEC, 0)) == -1) {
        p->fts_errno = errno;
        p->fts_info = FTS_ERR;
      } else
        p->fts_flags |= FTS_SYMFOLLOW;
    }
    return (p);
  }

  /* Directory in pre-order. */
  if (p->fts_info == FTS_D) {
    /* If skipped or crossed mount point, do post-order visit. */
    if (instr == FTS_SKIP || (ISSET(FTS_XDEV) && p->fts_dev != sp->fts_dev)) {
      if (p->fts_flags & FTS_SYMFOLLOW) (void)close(p->fts_symfd);
      if (sp->fts_child) {
        fts_lfree(sp->fts_child);
        sp->fts_child = NULL;
      }
      p->fts_info = FTS_DP;
      return (p);
    }

    /* Rebuild if only read the names and now traversing. */
    if (sp->fts_child && ISSET(FTS_NAMEONLY)) {
      CLR(FTS_NAMEONLY);
      fts_lfree(sp->fts_child);
      sp->fts_child = NULL;
    }

    /*
     * Cd to the subdirectory.
     *
     * If have already read and now fail to chdir, whack the list
     * to make the names come out right, and set the parent errno
     * so the application will eventually get an error condition.
     * Set the FTS_DONTCHDIR flag so that when we logically change
     * directories back to the parent we don't do a chdir.
     *
     * If haven't read do so.  If the read fails, fts_build sets
     * FTS_STOP or the fts_info field of the node.
     */
    if (sp->fts_child) {
      if (fts_safe_changedir(sp, p, -1, p->fts_accpath)) {
        p->fts_errno = errno;
        p->fts_flags |= FTS_DONTCHDIR;
        for (p = sp->fts_child; p; p = p->fts_link)
          p->fts_accpath = p->fts_parent->fts_accpath;
      }
    } else if ((sp->fts_child = fts_build(sp, BREAD)) == NULL) {
      if (ISSET(FTS_STOP)) return (NULL);
      return (p);
    }
    p = sp->fts_child;
    sp->fts_child = NULL;
    goto name;
  }

next:
  /* Move to the next node on this level. */
  tmp = p;

  /*
   * We are going to free sp->fts_cur, set it to NULL so
   * that fts_close() does not attempt to free it again
   * if we exit without setting it to a new value because
   * FCHDIR() failed below.
   */
  assert(tmp == sp->fts_cur);
  sp->fts_cur = NULL;

  if ((p = p->fts_link) != NULL) {
    fts_free(tmp);

    /*
     * If reached the top, return to the original directory, and
     * load the paths for the next root.
     */
    if (p->fts_level == FTS_ROOTLEVEL) {
      if (FCHDIR(sp, sp->fts_rfd)) {
        SET(FTS_STOP);
        return (NULL);
      }
      fts_load(sp, p);
      return (sp->fts_cur = p);
    }

    /*
     * User may have called fts_set on the node.  If skipped,
     * ignore.  If followed, get a file descriptor so we can
     * get back if necessary.
     */
    if (p->fts_instr == FTS_SKIP) goto next;
    if (p->fts_instr == FTS_FOLLOW) {
      p->fts_info = fts_stat(sp, p, 1);
      if (p->fts_info == FTS_D && !ISSET(FTS_NOCHDIR)) {
        if ((p->fts_symfd = open(".", O_RDONLY | O_CLOEXEC, 0)) == -1) {
          p->fts_errno = errno;
          p->fts_info = FTS_ERR;
        } else
          p->fts_flags |= FTS_SYMFOLLOW;
      }
      p->fts_instr = FTS_NOINSTR;
    }

  name:
    t = sp->fts_path + NAPPEND(p->fts_parent);
    *t++ = '/';
    memmove(t, p->fts_name, (size_t)(p->fts_namelen + 1));
    return (sp->fts_cur = p);
  }

  /* Move up to the parent node. */
  p = tmp->fts_parent;
  fts_free(tmp);

  if (p->fts_level == FTS_ROOTPARENTLEVEL) {
    /*
     * Done; free everything up and set errno to 0 so the user
     * can distinguish between error and EOF.
     */
    fts_free(p);
    errno = 0;
    return (sp->fts_cur = NULL);
  }

  /* NUL terminate the pathname. */
  sp->fts_path[p->fts_pathlen] = '\0';

  /*
   * Return to the parent directory.  If at a root node or came through
   * a symlink, go back through the file descriptor.  Otherwise, cd up
   * one directory.
   */
  if (p->fts_level == FTS_ROOTLEVEL) {
    if (FCHDIR(sp, sp->fts_rfd)) {
      SET(FTS_STOP);
      return (NULL);
    }
  } else if (p->fts_flags & FTS_SYMFOLLOW) {
    if (FCHDIR(sp, p->fts_symfd)) {
      saved_errno = errno;
      (void)close(p->fts_symfd);
      errno = saved_errno;
      SET(FTS_STOP);
      return (NULL);
    }
    (void)close(p->fts_symfd);
  } else if (!(p->fts_flags & FTS_DONTCHDIR) &&
             fts_safe_changedir(sp, p->fts_parent, -1, "..")) {
    SET(FTS_STOP);
    return (NULL);
  }
  p->fts_info = p->fts_errno ? FTS_ERR : FTS_DP;
  return (sp->fts_cur = p);
}

/*
 * Fts_set takes the stream as an argument although it's not used in this
 * implementation; it would be necessary if anyone wanted to add global
 * semantics to fts using fts_set.  An error return is allowed for similar
 * reasons.
 */
/* ARGSUSED */
int fts_set(FTS *sp, FTSENT *p, int instr) {
  _DIAGASSERT(sp != NULL);
  _DIAGASSERT(p != NULL);

  if (instr && instr != FTS_AGAIN && instr != FTS_FOLLOW &&
      instr != FTS_NOINSTR && instr != FTS_SKIP) {
    errno = EINVAL;
    return (1);
  }
  p->fts_instr = instr;
  return (0);
}

FTSENT *fts_children(FTS *sp, int instr) {
  FTSENT *p;
  int fd;

  _DIAGASSERT(sp != NULL);

  if (instr && instr != FTS_NAMEONLY) {
    errno = EINVAL;
    return (NULL);
  }

  /* Set current node pointer. */
  p = sp->fts_cur;

  /*
   * Errno set to 0 so user can distinguish empty directory from
   * an error.
   */
  errno = 0;

  /* Fatal errors stop here. */
  if (ISSET(FTS_STOP)) return (NULL);

  /* Return logical hierarchy of user's arguments. */
  if (p->fts_info == FTS_INIT) return (p->fts_link);

  /*
   * If not a directory being visited in pre-order, stop here.  Could
   * allow FTS_DNR, assuming the user has fixed the problem, but the
   * same effect is available with FTS_AGAIN.
   */
  if (p->fts_info != FTS_D /* && p->fts_info != FTS_DNR */) return (NULL);

  /* Free up any previous child list. */
  if (sp->fts_child) fts_lfree(sp->fts_child);

  if (instr == FTS_NAMEONLY) {
    SET(FTS_NAMEONLY);
    instr = BNAMES;
  } else
    instr = BCHILD;

  /*
   * If using chdir on a relative path and called BEFORE fts_read does
   * its chdir to the root of a traversal, we can lose -- we need to
   * chdir into the subdirectory, and we don't know where the current
   * directory is, so we can't get back so that the upcoming chdir by
   * fts_read will work.
   */
  if (p->fts_level != FTS_ROOTLEVEL || p->fts_accpath[0] == '/' ||
      ISSET(FTS_NOCHDIR))
    return (sp->fts_child = fts_build(sp, instr));

  if ((fd = open(".", O_RDONLY | O_CLOEXEC, 0)) == -1)
    return (sp->fts_child = NULL);
  sp->fts_child = fts_build(sp, instr);
  if (fchdir(fd)) {
    (void)close(fd);
    return (NULL);
  }
  (void)close(fd);
  return (sp->fts_child);
}

/*
 * This is the tricky part -- do not casually change *anything* in here.  The
 * idea is to build the linked list of entries that are used by fts_children
 * and fts_read.  There are lots of special cases.
 *
 * The real slowdown in walking the tree is the stat calls.  If FTS_NOSTAT is
 * set and it's a physical walk (so that symbolic links can't be directories),
 * we can do things quickly.  First, if it's a 4.4BSD file system, the type
 * of the file is in the directory entry.  Otherwise, we assume that the number
 * of subdirectories in a node is equal to the number of links to the parent.
 * The former skips all stat calls.  The latter skips stat calls in any leaf
 * directories and for any files after the subdirectories in the directory have
 * been found, cutting the stat calls by about 2/3.
 */
static FTSENT *fts_build(FTS *sp, int type) {
  struct dirent *dp;
  FTSENT *p, *head;
  size_t nitems;
  FTSENT *cur, *tail;
  DIR *dirp;
  void *oldaddr;
  size_t dnamlen;
  int cderrno, descend, level, nlinks, saved_errno, nostat, doadjust;
  size_t len, maxlen;
#ifdef FTS_WHITEOUT
  int oflag;
#endif
  char *cp = NULL; /* pacify gcc */

  _DIAGASSERT(sp != NULL);

  /* Set current node pointer. */
  cur = sp->fts_cur;

  /*
   * Open the directory for reading.  If this fails, we're done.
   * If being called from fts_read, set the fts_info field.
   */
#ifdef FTS_WHITEOUT
  if (ISSET(FTS_WHITEOUT))
    oflag = DTF_NODUP | DTF_REWIND;
  else
    oflag = DTF_HIDEW | DTF_NODUP | DTF_REWIND;
#else
#define __opendir2(path, flag) opendir(path)
#endif
  if ((dirp = __opendir2(cur->fts_accpath, oflag)) == NULL) {
    if (type == BREAD) {
      cur->fts_info = FTS_DNR;
      cur->fts_errno = errno;
    }
    return (NULL);
  }

  /*
   * Nlinks is the number of possible entries of type directory in the
   * directory if we're cheating on stat calls, 0 if we're not doing
   * any stat calls at all, -1 if we're doing stats on everything.
   */
  if (type == BNAMES) {
    nlinks = 0;
    nostat = 1;
  } else if (ISSET(FTS_NOSTAT) && ISSET(FTS_PHYSICAL)) {
    nlinks = cur->fts_nlink - (ISSET(FTS_SEEDOT) ? 0 : 2);
    nostat = 1;
  } else {
    nlinks = -1;
    nostat = 0;
  }

#ifdef notdef
  (void)printf("nlinks == %d (cur: %d)\n", nlinks, cur->fts_nlink);
  (void)printf("NOSTAT %d PHYSICAL %d SEEDOT %d\n", ISSET(FTS_NOSTAT),
               ISSET(FTS_PHYSICAL), ISSET(FTS_SEEDOT));
#endif
  /*
   * If we're going to need to stat anything or we want to descend
   * and stay in the directory, chdir.  If this fails we keep going,
   * but set a flag so we don't chdir after the post-order visit.
   * We won't be able to stat anything, but we can still return the
   * names themselves.  Note, that since fts_read won't be able to
   * chdir into the directory, it will have to return different path
   * names than before, i.e. "a/b" instead of "b".  Since the node
   * has already been visited in pre-order, have to wait until the
   * post-order visit to return the error.  There is a special case
   * here, if there was nothing to stat then it's not an error to
   * not be able to stat.  This is all fairly nasty.  If a program
   * needed sorted entries or stat information, they had better be
   * checking FTS_NS on the returned nodes.
   */
  cderrno = 0;
  if (nlinks || type == BREAD) {
    if (fts_safe_changedir(sp, cur, dirfd(dirp), NULL)) {
      if (nlinks && type == BREAD) cur->fts_errno = errno;
      cur->fts_flags |= FTS_DONTCHDIR;
      descend = 0;
      cderrno = errno;
    } else
      descend = 1;
  } else
    descend = 0;

  /*
   * Figure out the max file name length that can be stored in the
   * current path -- the inner loop allocates more path as necessary.
   * We really wouldn't have to do the maxlen calculations here, we
   * could do them in fts_read before returning the path, but it's a
   * lot easier here since the length is part of the dirent structure.
   *
   * If not changing directories set a pointer so that can just append
   * each new name into the path.
   */
  len = NAPPEND(cur);
  if (ISSET(FTS_NOCHDIR)) {
    cp = sp->fts_path + len;
    *cp++ = '/';
  }
  len++;
  maxlen = sp->fts_pathlen - len;

#if defined(__FTS_COMPAT_LEVEL)
  if (cur->fts_level == SHRT_MAX) {
    (void)closedir(dirp);
    cur->fts_info = FTS_ERR;
    SET(FTS_STOP);
    errno = ENAMETOOLONG;
    return (NULL);
  }
#endif

  level = cur->fts_level + 1;

  /* Read the directory, attaching each entry to the `link' pointer. */
  doadjust = 0;
  for (head = tail = NULL, nitems = 0; (dp = readdir(dirp)) != NULL;) {
    if (!ISSET(FTS_SEEDOT) && ISDOT(dp->d_name)) continue;

#if defined(HAVE_STRUCT_DIRENT_D_NAMLEN)
    dnamlen = dp->d_namlen;
#else
    dnamlen = strlen(dp->d_name);
#endif
    if ((p = fts_alloc(sp, dp->d_name, dnamlen)) == NULL) goto mem1;
    if (dnamlen >= maxlen) { /* include space for NUL */
      oldaddr = sp->fts_path;
      if (fts_palloc(sp, dnamlen + len + 1)) {
        /*
         * No more memory for path or structures.  Save
         * errno, free up the current structure and the
         * structures already allocated.
         */
      mem1:
        saved_errno = errno;
        if (p) fts_free(p);
        fts_lfree(head);
        (void)closedir(dirp);
        errno = saved_errno;
        cur->fts_info = FTS_ERR;
        SET(FTS_STOP);
        return (NULL);
      }
      /* Did realloc() change the pointer? */
      if (oldaddr != sp->fts_path) {
        doadjust = 1;
        if (ISSET(FTS_NOCHDIR)) cp = sp->fts_path + len;
      }
      maxlen = sp->fts_pathlen - len;
    }

#if defined(__FTS_COMPAT_LENGTH)
    if (len + dnamlen >= USHRT_MAX) {
      /*
       * In an FTSENT, fts_pathlen is an unsigned short
       * so it is possible to wraparound here.
       * If we do, free up the current structure and the
       * structures already allocated, then error out
       * with ENAMETOOLONG.
       */
      fts_free(p);
      fts_lfree(head);
      (void)closedir(dirp);
      cur->fts_info = FTS_ERR;
      SET(FTS_STOP);
      errno = ENAMETOOLONG;
      return (NULL);
    }
#endif
    p->fts_level = level;
    p->fts_pathlen = ftsent_pathlen_truncate(len + dnamlen);
    p->fts_parent = sp->fts_cur;

#ifdef FTS_WHITEOUT
    if (dp->d_type == DT_WHT) p->fts_flags |= FTS_ISW;
#endif

    if (cderrno) {
      if (nlinks) {
        p->fts_info = FTS_NS;
        p->fts_errno = cderrno;
      } else
        p->fts_info = FTS_NSOK;
      p->fts_accpath = cur->fts_accpath;
    } else if (nlinks == 0
#ifdef DT_DIR
               || (nostat && dp->d_type != DT_DIR && dp->d_type != DT_UNKNOWN)
#endif
    ) {
      p->fts_accpath = ISSET(FTS_NOCHDIR) ? p->fts_path : p->fts_name;
      p->fts_info = FTS_NSOK;
    } else {
      /* Build a file name for fts_stat to stat. */
      if (ISSET(FTS_NOCHDIR)) {
        p->fts_accpath = p->fts_path;
        memmove(cp, p->fts_name, (size_t)(p->fts_namelen + 1));
      } else
        p->fts_accpath = p->fts_name;
      /* Stat it. */
      p->fts_info = fts_stat(sp, p, 0);

      /* Decrement link count if applicable. */
      if (nlinks > 0 && (p->fts_info == FTS_D || p->fts_info == FTS_DC ||
                         p->fts_info == FTS_DOT))
        --nlinks;
    }

    /* We walk in directory order so "ls -f" doesn't get upset. */
    p->fts_link = NULL;
    if (head == NULL)
      head = tail = p;
    else {
      tail->fts_link = p;
      tail = p;
    }
    ++nitems;
  }
  (void)closedir(dirp);

  /*
   * If had to realloc the path, adjust the addresses for the rest
   * of the tree.
   */
  if (doadjust) fts_padjust(sp, head);

  /*
   * If not changing directories, reset the path back to original
   * state.
   */
  if (ISSET(FTS_NOCHDIR)) {
    if (len == sp->fts_pathlen || nitems == 0) --cp;
    *cp = '\0';
  }

  /*
   * If descended after called from fts_children or after called from
   * fts_read and nothing found, get back.  At the root level we use
   * the saved fd; if one of fts_open()'s arguments is a relative path
   * to an empty directory, we wind up here with no other way back.  If
   * can't get back, we're done.
   */
  if (descend && (type == BCHILD || !nitems) &&
      (cur->fts_level == FTS_ROOTLEVEL
           ? FCHDIR(sp, sp->fts_rfd)
           : fts_safe_changedir(sp, cur->fts_parent, -1, ".."))) {
    cur->fts_info = FTS_ERR;
    SET(FTS_STOP);
    return (NULL);
  }

  /* If didn't find anything, return NULL. */
  if (!nitems) {
    if (type == BREAD) cur->fts_info = FTS_DP;
    return (NULL);
  }

  /* Sort the entries. */
  if (sp->fts_compar && nitems > 1) head = fts_sort(sp, head, nitems);
  return (head);
}

static unsigned short fts_stat(FTS *sp, FTSENT *p, int follow) {
  FTSENT *t;
  dev_t dev;
  __fts_ino_t ino;
  __fts_stat_t *sbp, sb;
  int saved_errno;

  _DIAGASSERT(sp != NULL);
  _DIAGASSERT(p != NULL);

  /* If user needs stat info, stat buffer already allocated. */
  sbp = ISSET(FTS_NOSTAT) ? &sb : p->fts_statp;

#ifdef FTS_WHITEOUT
  /* check for whiteout */
  if (p->fts_flags & FTS_ISW) {
    if (sbp != &sb) {
      memset(sbp, '\0', sizeof(*sbp));
      sbp->st_mode = S_IFWHT;
    }
    return (FTS_W);
  }
#endif

  /*
   * If doing a logical walk, or application requested FTS_FOLLOW, do
   * a stat(2).  If that fails, check for a non-existent symlink.  If
   * fail, set the errno from the stat call.
   */
  if (ISSET(FTS_LOGICAL) || follow) {
    if (cowasm_stat(p->fts_accpath, sbp)) {
      saved_errno = errno;
      if (!cowasm_lstat(p->fts_accpath, sbp)) {
        errno = 0;
        return (FTS_SLNONE);
      }
      p->fts_errno = saved_errno;
      goto err;
    }
  } else if (cowasm_lstat(p->fts_accpath, sbp)) {
    p->fts_errno = errno;
  err:
    memset(sbp, 0, sizeof(*sbp));
    return (FTS_NS);
  }

  if (S_ISDIR(sbp->st_mode)) {
    /*
     * Set the device/inode.  Used to find cycles and check for
     * crossing mount points.  Also remember the link count, used
     * in fts_build to limit the number of stat calls.  It is
     * understood that these fields are only referenced if fts_info
     * is set to FTS_D.
     */
    dev = p->fts_dev = sbp->st_dev;
    ino = p->fts_ino = sbp->st_ino;
    p->fts_nlink = sbp->st_nlink;

    if (ISDOT(p->fts_name)) return (FTS_DOT);

    /*
     * Cycle detection is done by brute force when the directory
     * is first encountered.  If the tree gets deep enough or the
     * number of symbolic links to directories is high enough,
     * something faster might be worthwhile.
     */
    for (t = p->fts_parent; t->fts_level >= FTS_ROOTLEVEL; t = t->fts_parent)
      if (ino == t->fts_ino && dev == t->fts_dev) {
        p->fts_cycle = t;
        return (FTS_DC);
      }
    return (FTS_D);
  }
  if (S_ISLNK(sbp->st_mode)) return (FTS_SL);
  if (S_ISREG(sbp->st_mode)) return (FTS_F);
  return (FTS_DEFAULT);
}

static FTSENT *fts_sort(FTS *sp, FTSENT *head, size_t nitems) {
  FTSENT **ap, *p;

  _DIAGASSERT(sp != NULL);
  _DIAGASSERT(head != NULL);

  /*
   * Construct an array of pointers to the structures and call qsort(3).
   * Reassemble the array in the order returned by qsort.  If unable to
   * sort for memory reasons, return the directory entries in their
   * current order.  Allocate enough space for the current needs plus
   * 40 so don't realloc one entry at a time.
   */
  if (nitems > sp->fts_nitems) {
    FTSENT **new;

    new = realloc(sp->fts_array, sizeof(FTSENT *) * (nitems + 40));
    if (new == 0) return (head);
    sp->fts_array = new;
    sp->fts_nitems = fts_nitems_truncate(nitems + 40);
  }
  for (ap = sp->fts_array, p = head; p; p = p->fts_link) *ap++ = p;
  qsort((void *)sp->fts_array, nitems, sizeof(FTSENT *),
        (int (*)(const void *, const void *))sp->fts_compar);
  for (head = *(ap = sp->fts_array); --nitems; ++ap) ap[0]->fts_link = ap[1];
  ap[0]->fts_link = NULL;
  return (head);
}

static FTSENT *fts_alloc(FTS *sp, const char *name, size_t namelen) {
  FTSENT *p;
#if defined(FTS_ALLOC_ALIGNED)
  size_t len;
#endif

  _DIAGASSERT(sp != NULL);
  _DIAGASSERT(name != NULL);

#if defined(FTS_ALLOC_ALIGNED)
  /*
   * The file name is a variable length array and no stat structure is
   * necessary if the user has set the nostat bit.  Allocate the FTSENT
   * structure, the file name and the stat structure in one chunk, but
   * be careful that the stat structure is reasonably aligned.  Since the
   * fts_name field is declared to be of size 1, the fts_name pointer is
   * namelen + 2 before the first possible address of the stat structure.
   */
  len = sizeof(FTSENT) + namelen;
  if (!ISSET(FTS_NOSTAT)) len += sizeof(*(p->fts_statp)) + ALIGNBYTES;
  if ((p = malloc(len)) == NULL) return (NULL);

  if (!ISSET(FTS_NOSTAT))
    p->fts_statp =
        (__fts_stat_t *)ALIGN((unsigned long)(p->fts_name + namelen + 2));
#else
  if ((p = malloc(sizeof(FTSENT) + namelen)) == NULL) return (NULL);

  if (!ISSET(FTS_NOSTAT))
    if ((p->fts_statp = malloc(sizeof(*(p->fts_statp)))) == NULL) {
      free(p);
      return (NULL);
    }
#endif

  if (ISSET(FTS_NOSTAT)) p->fts_statp = NULL;

  /* Copy the name plus the trailing NULL. */
  memmove(p->fts_name, name, namelen + 1);

  p->fts_namelen = ftsent_namelen_truncate(namelen);
  p->fts_path = sp->fts_path;
  p->fts_errno = 0;
  p->fts_flags = 0;
  p->fts_instr = FTS_NOINSTR;
  p->fts_number = 0;
  p->fts_pointer = NULL;
  return (p);
}

static void fts_free(FTSENT *p) {
#if !defined(FTS_ALLOC_ALIGNED)
  if (p->fts_statp) free(p->fts_statp);
#endif
  free(p);
}

static void fts_lfree(FTSENT *head) {
  FTSENT *p;

  /* XXX: head may be NULL ? */

  /* Free a linked list of structures. */
  while ((p = head) != NULL) {
    head = head->fts_link;
    fts_free(p);
  }
}

static size_t fts_pow2(size_t x) {
  x--;
  x |= x >> 1;
  x |= x >> 2;
  x |= x >> 4;
  x |= x >> 8;
  x |= x >> 16;
#if LONG_BIT > 32
  x |= x >> 32;
#endif
#if LONG_BIT > 64
  x |= x >> 64;
#endif
  x++;
  return (x);
}

/*
 * Allow essentially unlimited paths; find, rm, ls should all work on any tree.
 * Most systems will allow creation of paths much longer than MAXPATHLEN, even
 * though the kernel won't resolve them.  Round up the new size to a power of 2,
 * so we don't realloc the path 2 bytes at a time.
 */
static int fts_palloc(FTS *sp, size_t size) {
  char *new;

  _DIAGASSERT(sp != NULL);

#ifdef __FTS_COMPAT_LENGTH
  /* Protect against fts_pathlen overflow. */
  if (size > USHRT_MAX + 1) {
    errno = ENAMETOOLONG;
    return (1);
  }
#endif
  size = fts_pow2(size);
  new = realloc(sp->fts_path, size);
  if (new == 0) return (1);
  sp->fts_path = new;
  sp->fts_pathlen = fts_pathlen_truncate(size);
  return (0);
}

/*
 * When the path is realloc'd, have to fix all of the pointers in structures
 * already returned.
 */
static void fts_padjust(FTS *sp, FTSENT *head) {
  FTSENT *p;
  char *addr;

  _DIAGASSERT(sp != NULL);

#define ADJUST(p)                                                   \
  do {                                                              \
    if ((p)->fts_accpath != (p)->fts_name)                          \
      (p)->fts_accpath = addr + ((p)->fts_accpath - (p)->fts_path); \
    (p)->fts_path = addr;                                           \
  } while (/*CONSTCOND*/ 0)

  addr = sp->fts_path;

  /* Adjust the current set of children. */
  for (p = sp->fts_child; p; p = p->fts_link) ADJUST(p);

  /* Adjust the rest of the tree, including the current level. */
  for (p = head; p->fts_level >= FTS_ROOTLEVEL;) {
    ADJUST(p);
    p = p->fts_link ? p->fts_link : p->fts_parent;
  }
}

static size_t fts_maxarglen(char *const *argv) {
  size_t len, max;

  _DIAGASSERT(argv != NULL);

  for (max = 0; *argv; ++argv)
    if ((len = strlen(*argv)) > max) max = len;
  return (max + 1);
}

/*
 * Change to dir specified by fd or p->fts_accpath without getting
 * tricked by someone changing the world out from underneath us.
 * Assumes p->fts_dev and p->fts_ino are filled in.
 */
#include<stdio.h>
static int fts_safe_changedir(const FTS *sp, const FTSENT *p, int fd,
                              const char *path) {
  int oldfd = fd, ret = -1;
  __fts_stat_t sb;

  if (ISSET(FTS_NOCHDIR)) return 0;

  if (oldfd < 0 && (fd = open(path, O_RDONLY | O_CLOEXEC)) == -1) return -1;

  if (cowasm_fstat(fd, &sb) == -1) goto bail;

  if (sb.st_ino != p->fts_ino || sb.st_dev != p->fts_dev) {
    errno = ENOENT;
    goto bail;
  }

  ret = fchdir(fd);

bail:

  if (oldfd < 0) {
    int save_errno = errno;
    (void)close(fd);
    errno = save_errno;
  }
  return ret;
}
